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Full text of "Handbook Of Chemical Engineering - I"

CHEMICAL ENGINEERING
out the entire number of hours represented by the abscissa. Hence areas under the curve represent kilowatt-hours. Thus if the line ba were straight, if its abscissa were 1,000 hr. and if the ordinates to b and a were 2,000 and 800 respectively, 1,400,000 kw.-hr. would have been generated during the 1,000 hr. of the year when the load was heaviest. Costs are laid off in quadrant (//): the hourly constant cost as Oci, the total cost when the load is a kilowatt as mai. Then the straight line CK^&I is drawn.
FIG,
Annual Load,hp.-hrs. 3.—Overhead and operating costs.
Wrter Wheel "^        =:
Loadjkw. FIG.  4.—Power costs for various capacities.
When the load is 6 kw., the cost per hour is 661.    Plot the curve in quadrant (///) a shown.    Then from the point d draw a horizontal line to intersect the cost line c\b\ a di.   Draw the vertical line from di and continue it by a circular arc around 0 as a center, then draw horizontally to intersect at dz the vertical line from d.   Then pdz represents the cost per hour when the load is pd.   Also the area Opd^q represents the total
Kitowcrt-te
FIG. 5.—Klingenberg chart.
cost of the 1,400,000 kw. hr. represented by the area Obdp.    During those hours of the year when the plant is heavily loaded, unit costs will be low.
These considerations may explain why, in buying power, rates may equitably vary according to the load factor proposed. A load which comes mainly at light-load periods is especially attractive to a company selling power, and it will ordinarily make low rates for such service. In all cases the effort is made to have the consumer pay his proportion of the constant costs of the generating plant, as well as those running costs which correspond with the incidence and duration of the load.
Overhead Charges.—Interest, taxes and insurance may be taken at 6, % to 2, and H per cent respectively. Depreciation may be based on the following estimated lives and residual values: